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Semirigid thermotropic liquid crystalline (LC) copolyesters, composed of a distyrylbenzene analogue of 1,3,4-thiadiazole (TD) and biphenyl, were prepared by high-temperature solution polycondensation and their LC and optical properties were examined. DSC measurement. polarizing microscope observation, and powder X-ray analysis indicated that the copolymers form smectic LC phases independent of polymer composition. Their mesophases were found to be more stable than those of the corresponding homopolymers. The copolymers with composition ratios of ca. 1 : 1 had the widest LC temperature ranges. UV-vis and PL spectral data in HFIP suggested that the polymers show absorption based on the distyrylbenzene analogue of TD and fluoresce blue light. No fluorescence was observed in solid state. [ABSTRACT FROM AUTHOR]